Very often, car owners have to deal with increased fuel consumption, loss of power, and sometimes even the complete failure of the car to move. Most often, this is caused by faulty fuel injectors due to the use of fuel of inadequate quality. And it doesn't matter whether this is caused by the driver's desire to save money on cheaper fuel or by the dishonesty of gas station employees. One way or another, the problem of the need to replace the injectors arises. The simplest one (and undoubtedly the most correct) the solution in this case is to contact the nearest specialized service station. However, if the car owner believes that he is capable of dealing with the problem on his own, undoubtedly saving some money in the process, the following tips are provided to help him, which will either help the car owner avoid mistakes during the work process, or convince him to abandon the useless undertaking in a timely manner.
First of all, it is necessary to clearly understand that the replacement process itself (described in the relevant chapter of this Manual) should only be performed by those with certain skills, as it may pose certain dangers to both health and life - the fuel pressure in some injection systems of modern engines can reach 250 atm, so any carelessness can have fatal consequences.
The second, no less important point is that even if the fuel injector is successfully replaced, there is a risk of ending up with an injector with a spray pattern of much worse quality than it had before the replacement, even if the replacement parts are of the highest quality. What can we say about cases of using low-quality or defective injectors?. It is precisely in order to avoid such situations that it is necessary to use special diagnostic stands available at service stations, or at least the simplest device, which will be discussed below.
First, you need to understand the structure of a diesel injector and the processes occurring within it. All injectors, with rare exceptions, are fundamentally similar, and the processes occurring in them are analogous. The fuel injector device is shown in the figure.
1. Intake chamber. 2. Nozzle body. 3. Nozzle nut. 4. Spacer. 5. Sprayer. 6. Spray needle. 7. Spray cavity. 8. Union nut for connection to high pressure pipeline. 9. Filter. 10. Drainage system nipple. 11. Injection pressure control gasket. 12. High pressure channel. 13. Spring. 14. Push pin.
The fuel injector operates as follows: fuel from the high-pressure pump (HPFP) enters the injector nozzle, and from there, through a system of channels (12), into the nozzle cavity (7). Further fuel flow is blocked by the nozzle needle (6), which is compressed by a spring (13). Meanwhile, the HPFP continues to pump fuel, raising its pressure to a level capable of overcoming the spring force and lifting the nozzle needle above its seat. At this point, fuel is injected into the cylinder, causing the pressure to drop again and the needle to seat, cutting off the fuel supply and locking the system. As fuel injection continues, the process repeats. The main operating condition in this case is that after the injection is completed, the system must close; otherwise, on the next stroke, fuel will be supplied not when the pressure in the system rises to the specified value, but at the moment the pump begins to supply fuel. The result will be rough engine operation, loss of power and failure of the fuel injector due to combustion products entering the unsealed system.
Knowing how the injector works, you can figure out what might be interfering with the normal locking of the system even though the parts appear to be in good working order. Most often, this is caused by the occurrence of lateral forces pressing the needle against the body of the sprayer. To combat such forces, a pressure pin (14) is located in the spacer (4). The pin relieves the needle from the potential impact of a deformed spring; however, if it has some wear, the pin itself can cause lateral force. Therefore, when replacing fuel injectors, you need to be prepared for the new nozzle to start "pouring", which will require repeated overhaul of the injector by turning over the spring or replacing it or the pusher. In some cases, it may even be necessary to replace the fuel injector housing.
Since the needle in the injector is not sealed, some fuel leaks between the needle and the injector body and into the cavity containing the spring (13). If fuel is not removed from this cavity, the injector needle may become stuck and the injector may become "locked." A drain system (10) is used to remove leaking fuel.
The opening pressure of the needle is adjusted by adjusting linings (11), and the entire structure is tightened by a union nut (4).
The nozzle does not contain any sealing elements, and tightness is ensured solely by precision machining of the mating surfaces. As a result, the main requirement when working with fuel injectors is sterile cleanliness. Immediately after unscrewing the high-pressure line from the injector, it is necessary to close the injector nipple with a clean and tight cap, since the smallest debris that gets into the injector nipple during testing on the bench will be driven inside by the fuel and can jam the nozzle needle. The injector cavity must always, whether before or after testing and adjustment, be absolutely protected from any dust, not to mention larger particles. In addition, any dirt that comes into contact with the injector when removing it can get into the channel and then damage the threads or disrupt the seal.
It is advisable to remove high-pressure pipelines in a package together with ties (if the engine design allows it), this way there will be less reason to puzzle over how it all happened. If it is not possible to remove the pipelines as a package, it is necessary to mark the first cylinder fitting on the pump, and also mark the pipelines themselves in the order in which they were installed.
After removing the injectors, it is necessary to check their functionality to ensure that the suspected cause of the engine malfunction is correct. The criteria for testing are as follows:
When fuel is supplied, the injector must open under a given pressure.
Fuel leakage from the spray nozzle is not allowed before the injector opens.
When spraying fuel, drops and jets are not allowed.
The spray pattern must be smooth, without deviations, and correspond to the direction of the hole (or holes) in a spray bottle.
After the fuel supply is stopped, the pressure in the injector should be maintained for some time (strictly speaking, the rate of decline of this pressure must be controlled).
The amount of fuel sprayed by the injectors of the different engine cylinders must be the same.
It is obvious that the fuel injector in the third measuring cylinder delivers less fuel than the other injectors.
It is also common to talk about the characteristic sound of the injectors operating, however, sound is not an objective parameter for evaluating injectors. This parameter cannot be ignored, but it should not be made the main one either.
Undoubtedly, the best way to check the performance of injectors is on a special stand. Design (and accordingly the cost) the design of such a stand can be very diverse, which will undoubtedly affect the accuracy of diagnostics and ease of use. Service stations may use electronically controlled test benches costing several thousand dollars, but if a car owner is determined to diagnose the injectors themselves, it is recommended to build a simple test bench themselves.
To do this, you will need to make a tee pipe, one end of which will be connected to one of the high-pressure nozzles of the fuel injection pump, the other to the fuel injector, and a pressure gauge with a scale of 200-300 atm must be attached to the third end.
A measuring vessel (ceiling glass) must be placed under the nozzle sprayer.
By turning the engine with the starter, you need to make sure that the injector starts to "fire", then, leaving the ignition on, turn the engine crankshaft manually, reading the pressure gauge (the process is tedious, but quite acceptable in the absence of other options).
In the vast majority of modern injectors, the opening pressure is regulated by selecting the thickness of the spacer washer between the spring and the body. Specialized workshops have sets of these washers to solve any adjustment problems. For car enthusiasts, it should be kept in mind that washers come in different diameters (for various injector bodies), and are available with or without a hole. Washers with a hole can always be used instead of washers without a hole, but the reverse substitution is not allowed. It is also unacceptable to use washers of the wrong diameter.
Typically, injectors are designed in such a way that increasing the thickness of the washer by 0.1 mm leads to an increase in injection pressure by 10 atmospheres (10 kg/cm² or 980 kPa). It is very common to see, when repairing injectors, that during previous interventions the injection pressure was regulated using pieces of razor blades placed under the spring. This method of regulation is completely unacceptable. Firstly, having a lining of uncontrolled shape creates uncertainty in the spring support and thus uneven spring development, which provokes the occurrence of lateral force. In addition, there is a risk of chipping a piece of the blade, which will lead to complete failure of the nozzle. The use of metal foil is also unacceptable, since gaskets made of soft material are completely short-lived. Therefore, the only high-quality solution to the problem should be recognized as the use of new adjusting washers of the calculated thickness.
Flushing and cleaning fuel injectors at home is strictly not recommended due to the futility of the undertaking.
The illustrations provided will make it easier to identify a particular fault. If you notice any abnormalities on your vehicle (extraneous noises, knocks, leaks, signs of uneven wear, handling problems, etc.) locate the location of the malfunction symptom, compare it with the drawing and refer to the table using the corresponding link. If it is not possible to determine the exact source of extraneous noise, then it is necessary to do this at least approximately. Then, using the illustrations and table, identify the specific fault.
The illustration and table below show the most common sources of noise, but similar symptoms may occur in other areas of the vehicle.
If it is not possible to determine the location of the fault from the drawing, then it is necessary to try to identify the cause using the main categories and points given in the table.
Note: In the figure, the following positions indicate:
- 13 - Front suspension shock absorbers
- 20 - Pedal assembly
- 6, 10 - Rear main gear reducer